Method of treating gelatin capsules and product resulting therefrom



Patented Dec. 18, 1951 METHOD OF TREATING GELATIN CAP- SULES AND PRODUCT RESULTING THEREFROM Blasey T. Palermo and Shelby 0. McMillion, Detroit, Mich., assignors to R. P. Scherer Corporation, Detroit, Mich., a corporation of Michigan No Drawing. Application March 5, 1949, Serial No. 79,908

Claims. 1

This invention relates to gelatin capsules adapted to contain liquid or gelatinous or viscous or granular material.

Conventional capsules made up of a composition consisting of gelatin, glycerin and water are relatively weak when first made. At this time the capsules retain the origiial water content of the composition used in making up the capsules. By drying, the capsules are rendered stronger. Under conditions of high humidity, the dried capsules tend to absorb moisture which renders the capsules flaccid or flabby. In other words, or such reabsorption of moisture, the capsules lose their resiliency. The reabsorption of moisture is accompanied by swelling, often to an objectionable extent.

We have now provided a method for treating gelatin capsules yielding a relatively high strength under conditions of low humidity and resulting moisture content and capable of reabsorbing moisture without loss of resiliency although such reabsorption renders the capsules weaker, i. e. breakable when subjected to relatively low pressures. Further, the capsules of the present invention can reabsorb water without objectionable swelling.

For carrying out the methods of the present invention, we may start with gelatin capsules prepared and filled by any conventional method, for instance, that disclosed in the patent to Scherer No. 1,970,396. The filled capsules are subsequently treated with a composition containing formaldehyde and thereafter dehydrated. The gelatin to plasticizer ratio in the capsules, the concentration and amount of the formaldehyde employed and other factors are adjusted as disclosed in greater detail hereinbelow, to confer on the capsules the desired strength under predetermined humidity conditions. Thus, we can treat the capsules to render them relatively strong under conditions of low humidity but relatively weak under conditions of high humidity. The so treated capsules are all relatively strong when first made, and retain their resiliency in spite of variations in breaking strength.

It is therefore an important object of the present invention to provide a method for treating gelatin capsules to render the capsules initially strong. resilient under various humidity condipose indicated and comprising subjecting capsules of adjusted gelatin and plasticizer ratio to the action of formaldehyde of specific concentration and in specific amounts followed by dehydration.

Other and further objects and features of the present invention will become apparent from the following description and appended claims.

In the following description, particular refer,- ence is made to the preparation of 6 minim capsules, although, obviously, capsules of other sizes may be made by the same methods. The strengths of these 6 minim capsules are defined, inter alia, in terms dry breaking strength and wet breaking strength. By the term dry. breaking strength we mean the force (in grams) required to break a capsule when applied parallel to the plane of sealing of the capsules (along the major axis of capsules prepared by the method of said Scherer patent) after the capsule has been treated with a formaldehyde containing composition, dried, for instance, at 80 F. and a relatively humidity of 25% and thereafter kept in air at 25% relative humidity. By the term wet breaking strength we mean the force (in grams) required to break a capsule when applied normally to the plane of sealing of the capsule after the capsule has been treated with a composition containing formaldehyde, dried, say, at 80 F. and a relative humidity of 25% and thereafter exposed, say, for 4 hours to an atmosphere of 80% relative humidity.

Filled capsules are first prepared by any suitable conventional method, for instance, that of the above mentioned patent to Scherer. The gelatin to plasticizer ratio of these capsules is maintained within limits disclosed hereinbelow. Especially when proceeding according to the method of said Scherer patent, the fresh filled capsules carry a thin film of oil. Although it is possible to remove this oil film, as by washing with naphtha, and also to dry the washed capsules slightly, we prefer to treat the fresh capsules in their original fresh condition. The thin oil film does not interfere with the subsequent treatment with the formaldehyde-containing 3 composition disclosed hereinbelow, and. actually serves the useful purpose of preventing adhesion between the fresh capsules which occasionally has been noted after removal of the oil film and before treatment with a liquid medium containing formaldehyde.

The mass of freshly prepared filled capsules obtained as described are next tumbled with an emulsion of formaldehyde in an oily medium. The amount and composition of this emulsion and the time of tumbling are disclosed in greater detail .hereinbelow. Preferably, the capsules are first placed in any suitable conventional tumbler and, while the capsules-are being tum bled, the emulsion is added and tumbling continued until the action of the emulsion has been completed to the desired extent. Then sponges (which may be saturated-with 'naphtha') may be placed in the tumbler and the tumbling may be continued, for removing the oily emulsion from the capsules. The capsules may then be dried, for instance, at 80 F. and 25% relative humidity for 72 hours, or in any other manner, until the desired dry breaking strength has been reached. Thereafter the capsules may be stored in a dry atmosphere (say, 25% relative humidity) to prevent reabsorption of moisture which would reduce the breaking strength, if such reabsorption is not desired.

The g'elatimplasticizer ratio and the effects due to variation thereof will be discussed in detail hereinbelow. Nevertheless, it should be noted at this time that a plasticizer is required and that the plasticizer employed is a polyhydric alcohol such as sorbitol or, in particular, glycerin. The resiliency of conventional gelatin capsules is due at least in part to their glycerin content.v The tendency of conventional gelatin capsules to absorb moisture (with resultant swelling and loss of resiliency) after drying is likewise due to their glycerin content. Such swelling and loss, of resiliency also takes place when ordinarygelatin capsules are exposed to aqueous formaldehyde solutions, whether conc'entrated or dilute, as by dipping, immersion, tumbling, spraying or otherwise. For this reason, we do not treat the gelatin capsules with an aqueous formaldehyde solution but use instead an emulsion of an aqueous formaldehyde solution in a liquid medium immiscible with water. The dispersed or emulsified formaldehyde solution is quite concentrated, being at least of 10% strength and preferably 35% or more. The liquid medium in which the formaldehyde solution is emulsified is preferably of limited or no volatility, so that the emulsioncan be preserved and used without change in concentration of CHOH (100% gaseous formaldehyde) due to evaporation of the dispersing medium. Examples of such water-immiscible liquids are the mineral and vegetable hydrocarbon and glyceride oils such as olive oil and light mineral oil. Glycerin dioleate may also be used Any suitable emulsifying agent may be used in an amount effective todisperse the formaldehyde solution. Ordinarily from about 5% to about 30% of emulsifying agent will suffice. Examples of such emulsifying agents are lanolin (the preferred emulsifying agent), lecithin, and the compounds of specific examples I to V of the patent to Katzman et al. No. 2,178,174. The ratio of formaldehyde solution to the dispersing medium or the total formaldehyde solution content 'of the emulsion will be discussed hereinblow;

As disclosed, emulsifying an aqueous formaldehyde solution in an oily medium serves to reduce the Water concentration in'the composition employed to treat the gelatin capsules and thereby prevents absorption of excessive amounts of Water by the capsules, at least before the capsules have been modified by the action of the formaldehyde. At the same time, the CI-IOH concentration in the dispersed formaldehyde solution is quite high so that the CHOH reacts readily with the gelatin capsules and all the capsules in one batch being treated receive the same treatment, i. e. their-breaking strengths will be the same. While the -"water concentration in an aqueous formaldehyde solution can be reduced by dilution with an organic solvent miscible with water,

for instance, acetone, we have noted that when aqueous foi mald'ehyde solutions diluted with acetone are used 'to treat a batch of gelatin capsules, the thus simultaneously treated capsule's do not consistently exhibit the same breaking strengths. We attribute this fact to the low CHOl-I concentration after dilution of the formaldehyde solution with acetone which we believe brings about slow and irregular action of CHOH on the gelatin.

Thus, a distinction should be made between an emulsion of an aqueous formaldehyde solution and a formaldehyde solution diiuted with an organic water miscible solvent. The emulsion and the solution may both have the same total CHOl-I concentration, but the emulsion will have its CHOH content confined to a single phase of the two phases .present, While the diluted solution will have its CHOH content dissolved in the total amount of liquid present. Thus, the CHOI-I is more concentrated and more reactive in the emulsion.

Another advantage flowing from the use of the emulsion is to be found in the fact that no oil removal by washing, (as with naphtha) isrequir'ed in the case of freshly prepared capsules which. can immediately be treated with emulsion.

Treatment of the capsules with the emulsion by way of tumbling is preferred, since by tumbling uniform contact of even small amounts of emulsion with thecapsules can be broughtabout. Thus, small amounts of emulsion can be used that are spent by tumbling with a single batch of capsules, and the problem of reuse of emulsion is eliminated. Nevertheless, if desired, the capsules may be dipped in emulsion, or agitated with an excess of emulsion, as long as provision is made for intimate contact and relative displacement as between capsules and emulsion.

The effect of the emulsion content of 37% aqueous CHOH is illustrated hereinbelow in the case of capsules made up from a composition containing 27% gelatin, 47.5% glycerin and 25.5% water. 20,000 filled 6 minim capsules freshly made'from this composite were tumbled with 200'grarns emulsion for 30 minutes. The emulsion contained 20% lanolin and 37% aqueous CHOH in the amounts tabulated hereinbelow, the remainder being light mineral oil. For comparison, one batch of" capsules was not tumbled with emulsion. After tumbling with emulsion, the capsules were tumbled with naphtha-soaked sponges and dried at 80 F. for the tabulated periods of time. The breaking strength of the capsules were determined before, during and after drying. The wet breaking strengths were determined after hours drying and 24 hours exposure to an atmosphere of 80 relative humidity.

ns-moss qThe above tabulated data illustrate a number of features of the methods-of the present inven- Ition (involving treatment of gelatin capsules with 'an emulsion of aqueous formaldehyde) First, the data show that, immediatelyjafter tumblingand before drying, the treated capsulesare much stronger than those not treated. Secondly, there is no very pronounced difference between "dry and wet breaking strength, unless the formaldehyde solution content of the emulsion exceeds Actually, when it is desired toprepare capsules having a dry breaking,strengthjdistinctly greater than the wet breaking strength, the ,emulsion should contain more than formaldehyde solution. At lower formaldehyde solution contents in the emulsion, the treated capsules are much stronger than untreated capsules before drying, while after dryingthe difference .in strength as between treated and untreated capsules is not quite so striking, although the treated capsules still are distinctly stronger than the untreated capsules. Further, at emulsion contents .of formaldehyde solution less than 0 7b. the wet'? breaking strengths of the treated capsules, while only slightly, if at all, below the dry breaking strength of the treated capsules, is much greater than that of the untreated capsulesgwhich lose their resiliency on exposure to moisture. Thirdly, in the case of capsules treated with emulsions containing 20% or more formaldehyde solution, there ,occurs a progressive reduction in dry breaking strength after more than 16 hours of drying, while this is not true of capsules treated with emulsions containing less formaldehyde solution or of untreated capsules. Finally, when 'the emulsion contains more than 20% of formaldehyde solution, increasing the formaldehyde solution content of the emulsion reduces both the dry and the wet breaking strength of the capsules V For certain purposes, for instance, coloring of oleomargarine, it is desirable to provide capsules having a high dry breaking strength and alow wet breaking strength. When dry, such capsules are strong enough to be handled, stored and shipped. When moist, the capsules'are weak enough (but still resilient) to be broken by'man ual pressure. In the case of 6 A; minim capsules, the dry breaking strength should be at least 500 grams and preferably about 1000 grams, "although the dry breaking strengtnmayrange as high as 2000 grams or higher! The wt" breaking strength should range from '200 grams to 1000 grams, a value of about 500 grams being preferred, For preparing such capsules, an emulsion should be used containing about 20% to 65% of formaldehyde solution, preferably about 50%.

The amount of emulsion used must be'sufllcient to insure uniform effect of the formaldehyde on the capsules, as illustrated by "the1fol-- lowing experiment wherein two batches (Wall 6 .fro'm the composition of Experiment 1) of 20,000 capsules each were tumbled, respectively with 200 grams and 100 grams of an emulsion containing 50% of 37% aqueous formaldehyde, 20% lanolin and 30% light mineral oil for 30 minutes.

Table 2 D Breaking Strength 1! Time, in

Hours 200 grams 100 grams Emulsion Emulsion 1o 2, 400 1, s00 24"" 2, 000 900 40. 1, 800 700 r 00. 1, 250 2,100 '420 400 1 41 1 At 80% R. H

As shown in Table 2, the results obtained when using grams of emulsion are quite erratic, probably due to the fact that each capsule in the lot has not-been affected exactly to the same extent as other capsules. V The time of tumbling of the capsules with the emulsion makes some difference but is ordinarily not critical, as, shown by the experiment of Table 3 hereinbelow. In this experiment, capsules made of the same composition as those of Experiments 1 and 2 were tumbled with 200grams of emulsion for each 20,000 capsules for various lengths of time. By way of comparison, dry breaking strengths are given both for treated and untreated capsules.

As shown, moreprolonge'd tumbling tends to reduce the dry breaking strength somewhat. We prefer to tumble for at least 20 minutes, for the practical reason that by this time most of the formaldehyde fumes have been dissipated so that the capsules are more easily handled; a r

The influence of the gelatin to plastzicizer ratio in the composition making up the capsules is quite important, as illustrated in the experiment of Table 5 where the ratio of gelatin to glycerin is varied. Batches of 20,000 capsules each were tumbledfor 30 minutes with 200 grams of an emulsion containing 50% of 37% aqueous form'- aldehyde, 20% lanolin and 3.0% light mineral oil. In the experiment of Table 5, gelatin compositions were used made up of the following in- "sredi nts:

' Table 4 composition Per Cent Per (lent Per'Oent fi a Gelatin Glycerin Water Glycerin 19. 057 41. 983 2. 05 22. i0. 435 1. 690 25. 080 38. 390 1. 435 27.787 37.708 1.245 47.5 g 25.5 0.56s

while the reverse is true of a low ratio.

, Inr'Table 4 v, and elsewhere-in athis specification, and in: the claims, the-percentages ofvgelatin, ,glyce erin and-water specified for the capsuleeiorming compositions are :absoluterpercentages. For .in*

stance, in the 7 case of the water, ithecpercentage indicates the total'rwaterrcontent including the water added as such, the moisture content of the gelatin (ordinarily about 9% to 13% and commonly about 11%) and the water content of the glycerin (in the ease of U; 'S. I. glycerin, 5%).

Gelatin and glycerinpercentayes indicate these substances in water-free form. Thus, Composition 5 of Table 4 (which includes a total water content of 25.5%) may be made up by adding about 20% water to gelatin of 11% moisture content and Ups. P. glycerin of 5% water content.

Table .5

As shown by the data in Tables 4 as 5, a high ratio of gelatinto glycerin brings about both a high dry and a'high Wet breaking strength, When both high dry strength and intermediate or low wet strength are desired (as in the case of capsules to .be used ,for coloring oleomargarine), the emulsion should contain more than 20% but less than. 65% formaldehyde solution and the gelatin to elycerinratio should amount to about Attention is directed to the factjthat the wet f :strengths of Table have been determined after 90 hours at 80% relative humidity, while those of Table 1 were determined after 2411101115 at.';8 0%

relative humidity. These values in the twotables are therefore not strictly comparable.

Another point 'of interest brought -.out by :the :data of figureliis the effect of immersionjn-water on thetreated capsules. As shown, such --immersion greatly reduces the breaking strength,

but the resiliency of the capsules is;not,- destr 0yed.

Thus, 1 even capsules of :very great .dry breaking strength can be rendered breakable by :manual apressure .byimmersion in water, if zso desired.

,The characteristic changesin breaking strength a brought-about by changes in=moisture=contentlof capsules treated according to the present invention are :clearly brought out .aby gthecdata in Table '6. In the-experiment of Iabl e 6.:capsuljes were prepared and treated as in the experiment of Table 1 with an emulsion containing 50% of 37% aqueous formaldehyde. The breaking strength of the capsules was determined from time to time as the capsules were first dried at 80 F. and a relative humidity of 25% for 90 hours, then 'storedfor three weeks at room temperature at a relative humidity of 25%,--there .after kept for 25 hours at a relative humidity of 80% and finally kept in a desiccator-overphosphorus pentoxide for 15 hours.

for eac 00 ca su e Tcbl.e .6

( ours Total Time Breaking Condition ig i (Hours) Strength Specific Elapsed Condition 180 F. 25% RSH 0 0 6, 470 D0 1% a 1% 9 p0 5 5 3,200 JD? 1. 10 1 Do e 15 2,400 11 9? 1 D0,. 25 V 2, 000 "Do a0 1,909 "Do 35 1,820 ,Do 40 1, 800 Do 90 1 90 11,250 Room Temp. 25% R. H- 0 90 1, 250

-.,Do 5 04 594 4,140 i 0 I :594 7 1,140 5. 3 15 "609 .440 2c 614 30 25 619 420 '0 619 l .420 5 624 .500 0 629 750 15 634 1,070

' Asshownbyth tabulated data, the initial drying "reduces the breaking strength from about 6400gramsto 1250 grams. Aifurtherslight rednction to 1140 grams occurs during dry storage.

Exposure to a humid atmosphere reduces the breaking strength to 420 grams, but dehydration over phosphorus pentoxide rapidly restores the breaking strength to'a value' of 1070 grams. 'Note that breaking strength ,and resiliency are not completely lost on humidification and are rapid- 1y r covered o deh dra ont r o ehydration after 'humidification, the capsules are not distorted asby formation of dimples. In the case of conventional capsules, on the other hand, um ifieation cause ob e ona l w lin 01' even bursting, and subsequent dehydration often brings about distortion.

It .willthus be seen that we'have provided a method for treating capsules made up of aqueous plasticized gelatin compositions whereby the capsules are j rendered initially strong and whereby thebreaking strength can be varied at will by changing the humidity conditions to which the apsules a e subje ted.

ln general our process may be described as directed to the treatment of gelatin capsules in hi h he ge atin to l sticizer (or gelati .12 glycerin) ratio does not exceed 1.5 and ,doespnot ta below 0. hetr tment m y b salute include contacting theicapsules, p efer bl y tumbli g. wi lan s on of a ueous forma1-' dehyde for at least a few minutes (2 or 3 minutes'), There is no critical upper limit for lithe contact time, although, .of course, when small ,amounts of emulsion are used, the exhaustion of the formaldehyde content may render longer c ntact.timespoi ess- Th emul on ma contain about from 20 to% aqueous formaldehyde so ut o o t eas i ib s .re eth. p ierably at least 35%. ,A-sufiicient amount of emulsionshouldj be used to insure uniform action on theeapsules. 1n the-caseof 6 /2 minim capsules,

er tha te m .o mu sio shou be used For capsules of. other s es. am u of mulsion. sh u b ed; .n-n t0- portion to the surface of the capsules to be treated, Dehydration after treatment maybe effected either ,by drying at a slightlyelevated temperature .in a ,dr atm sp r .o yrea ment with a water absorbent liquid such as,ace ,ftone- Many details of composition and procedure can be varied within a wide range without departing from the principles of this invention and it is therefore not our purpose to limit the patent granted on this invention otherwise than necessitated by the scope of the appended claims.

We claim:

1. A method of treating capsules made up of an aqueous composition comprising from about 25% to 42% water together with gelatin and glycerin in a ratio ranging from 0.5 to 1.5, said method comprising tumbling said capsules having said water content for at least about two minutes with an aqueous emulsion containing from 20% to 65% of aqueous formaldehyde of at least 10% strength dispersed in a water-immiscible non-volatile oil.

2. A method of treating capsules made up of an aqueous composition comprising gelatin and glycerin in a ratio ranging from 0.5 to 1.5 and containing from about 25% to 42% watensaid method comprising tumbling said capsules having said water content for at least about two minutes with an aqueous emulsion containing from 20% to 65% of aqueous formaldehyde of at least 10% strength dispersed in a water-immiscible nonvolatile oil and thereafter reducing the water content of said capsules substantially below the amount of water present in said capsules before said tumbling.

3. A method of treating capsules made up of an aqueous composition comprising gelatin and glycerin in a ratio ranging from 0.5 to 1.5 and containing from about 25% to about 42% water, said method comprising tumbling said capsules having said water content for at least about two minutes with an aqueous emulsion containing from 20% to of aqueous formaldehyde of at least 10% strength dispersed in a water-immiscible non-volatile oil, thereafter reducing the water content of said capsules substantially below the amount of water present in said capsules before said tumbling, and thereafter maintaining the dehydrated capsules in a dry atmosphere.

4. Capsules made up of an aqueous composition comprising gelatin and glycerin in a ratio ranging from 0.5 to 1.5 and characterized by relatively high breaking strength when containing relatively small amounts of moisture and characterized by a relatively low breaking strength when containing relatively large amounts of moisture, said capsules having been prepared according to the method of claim 1.

5. A 'method according to claim 1 for treating edible capsules comprising after said tumbling removing residual oily emulsion from said capsules by contacting said capsules with sponges saturated with naphtha.

BLASEY T. PALERMO. SHELBY C. MoMILLION.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,898,507 Stein Feb. 21, 1933 2,255,694 Beale Sept. 9, 1941 

1. A METHOD OF TREATING CAPSULES MADE UP OF AN AQUEOUS COMPOSITION COMPRISING FROM ABOUT 25% TO 42% WATER TOGETHER WITH GELATIN AND GLYCERIN IN A RATIO RANGING FROM 0.5 TO 1.5, SAID METHOD COMPRISING TUMBLING SAID CAPSULES HAVING SAID WATER CONTENT FOR AT LEAST ABOUT TWO MINUTES WITH AN AQUEOUS EMULSION CONTAINING FROM 20% TO 65% OF AQUEOUS FORMALDEHYDE OF AT LEAST 10% STRENGTH DISPERSED IN A WATER-IMMISCIBLE NON-VOLATILE OIL. 